A yarn knotter of the type which the present invention is concerned comprises a suction pipe having a suction opening which can receive the yarn ends and which is formed with a clamping seat against which a clamping body or member can move to engage the yarn ends against the seat after they have been sucked into the suction tube.
Earlier devices of this type utilize a suction tube with a widened tube end receiving the clamping member and which can be biased in the clamping or clamp-closing direction by a spring. To permit the yarn ends to be drawn by suction into the tube, the clamping body is drawn away from the seat by a lever and a bowden cable cooperating with the lever which is articulated to the clamping member. This allows the suction in the tube to reach the orifice at which the yarn ends are drawn into the tube. Thereafter, the bowden cable is so actuated that the clamping spring moves the clamping body into the clamping position to retain the yarn ends. This knotting device is expensive and unreliable since it is prone to mechanical failure. Tangling of yarn ends is also a problem.
In another arrangement the suction end of the suction tube has a clamping body shiftable between axial limits and traversed by a suction opening. The closing force here is also generated by a spring and the suction generated in the tube moves the clamping member against the force of the spring to unblock the suction opening in particular. The yarn ends can thus be drawn into the suction opening.
Because the suction opening remains open only as long as the suction force can act upon the clamping body against the spring force, suction must be applied for a considerable length of time and, because at least part of the suction force must counteract the spring force, the energy required to generate the suction at the pump is only partially utilized for drawing the yarn ends into the tube. This system is also not fully reliable and requires enhanced suction capabilities of the suction pump as well as increased operating costs.